Localization of hydroxyindole O-methyltransferase-synthesizing cells in bovine epithalamus: immunocytochemistry and in-situ hybridization

Abstract

Hydroxyindole O-methyltransferase (HIOMT)-immunoreactive cells and melatonin synthesis were demonstrated in bovine epithalamus (including the pineal gland) with monoclonal antibodies and cRNA probes to HIOMT. The HIOMT-immunoreactive product was present in the cytoplasm of pinealocytes. All identifiable pinealocytes were clearly labeled in the pineal gland. The expression of the HIOMT gene was first identified in pinealocyte cytoplasm by in-situ hybridization (ISH). The distribution of the hybridization-positive cells in the pineal gland was compatible with that revealed by immunocytochemistry using the monoclonal antibody to HIOMT. In addition, HIOMT transcripts were found in the medial habenular nucleus, and the habenular and posterior commissure; they may correspond to S-antigen-immunoreactive cells demonstrated in the same regions of the hamster and the mouse. In these regions, the hybridization-positive cells did not exhibit HIOMT-immunoreactivity; thus, cells devoid of immunoreactivity may synthesize but rapidly transport the newly synthesized proteins. These results indicate (1) that the conversion of N-acetylserotonin into melatonin takes place in the cytoplasm of pinealocytes, (2) that some epithalamic cells in the habenular area may synthesize melatonin, and (3) that melatonin may act as a chemical messenger in centrally directed processes, as shown by using S-antigen immunocytochemistry.

Distribution of hydroxyindole-O-methyltransferase mRNA in the rat brain: an in situ hybridisation study

“…The expression of HIOMT in the cells of the stalk and deep pineal demonstrates that they are able to synthesise MEL. S-antigen -immunoreactivity has indicated that pineal cells of the deep pineal project to adjacent central areas of the brain in some species, such as the Djungarian hamster (Korf et al 1986), the mouse (Korf et al 1990) and cattle (Sato et al 1991), but not in the hedgehog, Mongolian gerbil, cat or rat (Korf et al 1985). In the present study, we have not observed extra-pineal labelling resulting from axon-like projections of pinealocytes, thus confirming the findings in the rat as reported by Korf et al (1985).…”

Macro-microscopical aspects of the buffalo (Bubalus bubalis Linnaeus, 1758) pineal gland

“…The animal with the largest live weight and metabolic weight (number 10) possessed a pineal gland of weight (265mg) close to that of the mean value (251.4 ± 83.1mg) presented in this study, confirming the study of Volrath (1979) where the metabolic weight has no influence on the pineal weight. Sato et al (1991) further states that the cells present in the habenular commissura possess secretory activity and that the pineal gland of the bovine communicates with the third ventricle. In a similar manner, in buffalos, the gland communicates with the lumen of the stem and the third ventricle.…”

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…In some rodent species the sympathetic fibers spread out of the pineal gland toward the habenular nuclei (Korf et al, 1990). In some species, a few pinealocytes of the deep pineal gland project to neighboring central structures (the habenular nucleus, the pretectal areas) where they make synapses (Korf et al, 1986(Korf et al, , 1990Sato et al, 1991). The putative transmitters involved have not been identified, but this observation suggests that the pineal gland could exert its influence by a neuronal pathway in addition to the MEL endocrine pathway.…”